Kinetics and mass transfer in a direct methanol fuel cell

Fuel cell researchers often use polarization curves to characterize the performance of their systems. These measurements give a good indication of the overall power output of the fuel cell, but do not allow for direct analysis of the various losses in the system. To make improvements in Direct Methanol Fuel Cells (DMFCs) the origin and magnitude of the different losses in the cell need to be quantified for different operating conditions. This work outlines methods to characterize DMFC performance using experimental and modeling techniques.; A 1-D model was developed to describe various aspects of DMFC kinetics and mass transfer. This model accounts for the complex reaction mechanism of methanol oxidation at the anode, mass transfer resistance, diffusion, crossover of methanol and the mixed potential of the oxygen cathode due to methanol crossover. The model was able to reasonably predict the experimental data for methanol concentrations between 0.05 M and 2 M.; The individual voltage losses accounted for all of the voltage loss observed during the operation of the full cell. The anode and cathode activation accounted for most of the losses. It is shown that cells operated at constant cathode stoichiometry or low cathode flow rate can show a parabolic shape in the methanol crossover due to the electroosmic drag dominance over diffusion as the primary transport mechanism for methanol through the membrane. Conversely, sufficient high cathode flow rate will increase the diffusion in the membrane making the methanol crossover curve more linear in shape.; Niobium was doped into anatase TiO2 support at 10 mol% (Nb0.1Ti 0.9O2) using solgel chemistry. A PtRu/Nb0.1Ti 0.9O2 catalyst was synthesized by LiBH4 reduction in THF. The methanol electrooxidation activity of the catalyst shows that this oxide support was electrically conductive. The current (A/gPt) was 6% higher on the PtRu/Nb0.1Ti0.9O2 catalyst compared to a commercial PtRu/C catalyst at 25°C. The electrochemically active surface area of the PtRu/C was 94% higher than PtRu/Nb0.1Ti0.9O 2, thus the current per active site was 100% higher on PtRu/Nb 0.1Ti0.9O2. A membrane electrode assembly with PtRu/Nb0.1Ti0.9O2 had 46% higher current (A/gPt) than an equivalent E-TEK MEA at 70°C.